Proton pump inhibitors represented by omeprazole, which suppress secretion of gastric acid for the treatment of peptic ulcer, reflux esophagitis and the like, have been widely used in clinical situations. However, the existing proton pump inhibitors are associated with problems in terms of effect and side effects. To be specific, since the existing proton pump inhibitors are unstable under acidic conditions, they are often formulated as enteric preparations, in which case several hours are required before expression of the effect. In addition, since the existing proton pump inhibitors show inconsistent treatment effects due to metabolic enzyme polymorphism and drug interaction with pharmaceutical agents such as diazepam and the like, an improvement has been desired.
As pyrrole compounds having a proton pump inhibitory action, EP-A-0259085 describes a compound represented by the formula:
and the like.
As a production intermediate for a compound having a CCK antagonistic action, WO92/04025 describes a compound represented by the formula:

As compounds having a thromboxane A2 (TXA2) antagonistic action and a TXA2 synthase inhibitory action, JP-A-8-119936 describes a compound represented by the formula:
wherein r1 is carboxy, protected carboxy, carboxy(lower)alkyl, protected carboxy(lower)alkyl, carboxy(lower)alkenyl or protected carboxy(lower)alkenyl, r2 is hydrogen; lower alkyl; heterocyclic (lower)alkyl optionally having aminoimino or protected aminoimino; heterocyclic (lower)alkenyl; or heterocyclic carbonyl, r3 is hydrogen or lower alkyl, r4 is acyl, r5 is hydrogen, A0 is lower alkylene, and Z0 is S or NH, provided when r1 is carboxy or protected carboxy, then Z0 is NH.
Moreover, as a therapeutic drug for neoplastic diseases or autoimmune diseases, WO2004/103968 describes a compound represented by the formula:
wherein r6 is aryl, aralkyl or heteroaryl, r7 is aryl or heteroaryl, and r8 is aryl, heteroaryl or an optionally substituted aminomethyl.
A pharmaceutical agent that effectively suppresses gastric acid secretion as known proton pump inhibitors, which is improved in instability under acidic conditions, dispersion of effects due to metabolic enzyme polymorphism and drug interaction, which are problems of known proton pump inhibitors, is expected to show more superior treatment effect on peptic ulcer, reflux esophagitis and the like. As the situation stands, however, a proton pump inhibitor capable of sufficiently satisfying these requirements has not been found. It is therefore an object of the present invention to provide a compound having a superior acid secretion suppressive effect (particularly, an acid secretion suppressive effect based on proton pump inhibition), which has been improved in these problems.